1. Field of the Invention.
The present invention relates generally to methods and apparatus for cooling plastic containers formed by stretch blow molding of plastic parisons, and more particularly relates to methods and apparatus for cooling plastic containers by introducing cryogenic liquids within such containers soon after their formation.
2. Description of the Prior Art.
Current methods and apparatus for cooling stretch blow molded plastic containers include the use of liquid cooled molds for standard containers and swirled air for heat set containers. In addition, there are known methods and apparatus utilizing cryogenic gases to cool stretch blow molded containers, where cryogenic liquids are vaporized and blown into containers at high pressures of typically between about 25 and 30 bar, thereby cooling the containers through conduction and convection such as described in U.S. Pat. Nos. 4,039,641; 5,229,043; and 5,730,914.
Known methods and apparatus also utilize cryogenic liquids introduced within stretch blow molded containers for purposes of cooling, such as described by U.S. Pat. Nos. 3,065,501; 4,367,187; 4,883,631; 5,018,358; 5,085,822; 5,101,636; and 5,182,122. Such cryogenic liquid methods and apparatus generally do not require the high delivery pressure of methods and apparatus that utilize cryogenic gas to cool stretch blow molded containers, thereby eliminating the need for a muffler system for the consequent loud exhaust gases. Moreover, cryogenic liquid cooling of stretch blow molded containers is more efficient than a cooling utilizing either air or cool gases.
However, despite the availability of such methods and apparatus, there exists a need in the art for methods and apparatus that introduce cryogenic liquid within stretch blow molded containers for cooling, yet are capable of providing a pulse of cryogenic liquid after a preselected time subsequent to formation of the container, in order to provide rapid, uniform and efficient cooling. A pulse of cryogenic liquid is intended to mean a measured quantity of cryogenic liquid at a preselected temperature and preselected pressure delivered during a predetermined time interval.